Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 401 of 707

Another problem typically encountered is nonuniformity of finish, which is normally the result of inadequate precleaning. Black phosphate conversion coatings are very economical to apply with an aver- age applied cost of about 2 to 4 cents per square foot. Black zinc phosphate conversion coatings offer the following benefits: 1.Low application cost. 2. Little appreciable dimensional change. 3. Ease of application. 4. High-corrosion resistance at a low cost. In conclusion: all three of these blackening methods—hot alkaline black oxi- dizing, oxidizing, room-temperature black oxide, and black zinc phosphate—offer the metal finisher a decorative, moderately corrosion-resistant black finish at an economical cost with little dimensional change. The ability to apply these finishes in bulk and the simple basic equipment used to apply these finishes make them viable alternatives to painting and/or plating. 400

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